Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $73.62   4.199%   $76.7113   $76.71   $76.70   $76.70  
  Purchase #2 $55.49   8.591%   $60.2571   $60.26   $60.25   $60.30  
  Purchase #3 $166.62   11.805%   $186.2895   $186.29   $186.30   $186.30  
  Purchase #4 $205.71   4.533%   $215.0348   $215.03   $215.05   $215.00  
  Purchase #5 $78.78   3.565%   $81.5885   $81.59   $81.60   $81.60  
  Purchase #6 $192.26   10.799%   $213.0222   $213.02   $213.00   $213.00  
  Purchase #7 $235.66   7.316%   $252.9009   $252.90   $252.90   $252.90  
  7 purchase totals = $1,008.14       $1,085.8043   $1,085.80   $1,085.80   $1,085.80